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., ...:Z;.',?"''!'!;'. . . .' . '. .' ';.i,' ~' ~ ' '.' ,'. . ",:-i.dZ,"",.':,.u;'. : 0019~8 . ' Question 7: Based on the limited grouting performed to-date, does the Board: a. Concur with the location, extent, and approach used to evaluate the need for blanket grouting below the zone 1 core at its contact with the Lewis Shale? Response: Yes, The CRB concurs with the blanket grouting location, extent, and approach being developed for the Lewis Shale beneath the zone 1 core. It is important that shallow joints and fractures be sealed to prevent undesirable seepage flows near the contact of the zone I core and the foundation. Maximum spacing of these primary grout holes should be 40 it, as proposed. Split spacing should proceed as needed and indicated by grout takes in the primary holes. b. Concur with the approach and procedures used to assess and complete stitch/feature grouting of specific discontinuities in the foundation? Response: . Yes. The CRB concurs with the stitch grouting of the open joints which tend to trend diagonally from upstream to downstream beneath the zone 1 core section of the dam. It is important that features that are capable of conducting seepage from upstream to downstream be sealed to protect the core section of the dam. c. Concur with the procedures used to perform the blanket and curtain grouting? Response: In general, the CRB agrees with the procedures but with some caveats. There are saine very large grout takes being experienced in the Lewis Shale at considerable depth beneath the valley floor. The CRB recommends that criteria be provided to the grout inspectors with regard to initiation of grout thickening to a more stable grout mix soon after it becomes obvioUs that a hole has very little tendency to be tightening under the thin initial mix. Tills thickening should continue at intervals until a mix is obtained which will result in reaching tight refusal. The CRB believes that a grout curtain also serves the puipose of exploration of foundation conditions. Where large grout takes occur, we recommend that investigations be undertaken to try and identify the cause of the large injection of grout. Tills should lead to a foundation interpretation, which may facilitate improved treatment and allow a determination as to whether or not' the feature or features have any implications, which need further remediation. As the geologic interpretation progresses, it may be necessary to do further subsurface investigations by taking appropriately located and oriented core borings. In this event, the investigations would likely need to include both vertical and inclined borings. Specialty tools, such as triple tube core barrels, straddle packer pressure tests, and Acoustical Televiewer CATV) bore hole surveys may be needed to supply -5-